After an Rx11 flush the vacuum hangs at 1500–2500 µ and won't reach 500

Tools: Nitrogen with regulator, hoses, catch container, heat gun, micron gauge

1. What Rx11 Flush is: an HFC-based solvent (the maker lists a boiling point around 106 °F at atmosphere). Under vacuum it boils easily, but a PUDDLE in a coil bend, in the accumulator or a low loop of the line set evaporates slowly — there's no heat for boiling, the metal cools. Until the puddle boils off, the microns hang at 1500–2500 and barely move. Water behaves exactly the same.
2. Sign of residue: with the pump valved off the curve rises fast and LEVELS OFF at one value (the puddle's vapor pressure at its temperature — it can be far above 2500 µ; for water at 72–80 °F it is 20,000–25,000 µ) instead of climbing steadily. Warm a spot — microns jump up and then start falling: you found the puddle.
3. Flushing done right: each component SEPARATELY (evaporator, condenser, liquid line, suction line); compressor, TXV/piston, filter drier and accumulator disconnected or bypassed — never flush through them. Inject Rx11 from its own can through the maker's injection valve into a system with NO pressure; NEVER connect the can to nitrogen — it can burst. Then disconnect the can and push the flush through with nitrogen at about 120 psig until clear liquid with no oil or dirt comes out. Catch it in a container, not on the ground.
4. The purge afterwards is the key: dry nitrogen through each component until no mist/drops come out. 5–10 minutes per component minimum, a long line set or big condenser — 15. Hold a paper towel at the outlet: dry — done. Purge in the flow direction, bottom-up where possible, to carry puddles out.
5. Then: a new filter drier (mandatory — the old one absorbed solvent and water), a suction clean-up drier on a dirty system, micron gauge on the system, evacuate.
6. If the microns still hang at 1500–2500: warm the lower coil bends, the accumulator, the low points of the line set with a heat gun (up to 150 °F on the metal) — the solvent boils off in minutes; triple evacuation: pull → nitrogen 5–10 psi for 10 minutes → release → pull, three cycles. Nitrogen “carries out” vapor that won't pull on its own.
7. Normal at the end: holds ≤500 µ for 10 minutes (POE) with the pump valved off. The maker gives no “safe” residue level: the flush is removed fully with nitrogen and vacuum. No need to chase 100 µ.
8. What happens if some residue stays. The maker only says Rx11 “will not attack components” and that leftover solvent boils off under vacuum; it gives no allowable percentage. Solvent left in the circuit thins the oil (worse compressor lubrication), pressures don't match the chart, subcooling looks “odd”, the TXV may hunt; with moisture present — a risk of acid. Sign of too much: after a weighed-in charge the pressures and SH/SC don't match the chart with no visible cause, oil in the sight glass dark and thin. Fix: recover, new filter drier, nitrogen purge, proper evacuation, recharge by weight. Off-label solvents (brake cleaner, acetone, mineral spirits) — never in a system: they attack seals and leave a residue that won't boil off.
9. How to tell HOW MUCH stayed. Exactly — only a lab; in the field, three estimates. 1) Scale during the flush: weigh the Rx11 canister before and after (what went in), weigh the catch container (what came out) — the difference minus what left during the nitrogen purge (usually almost all of it) is the residue; compare with the factory charge in oz. 2) Refrigerant identifier: it samples VAPOR and reads refrigerant purity and air. The flush boils far higher than the refrigerant (106 °F), so little of it is in the vapor — a good reading does NOT prove there is no flush left; a bad one is a reason to recover and recharge. 3) Standing pressure: charge weighed in, unit off and cooled, compare the pressure with the chart at the coldest component's temperature: the solvent boils far higher than the refrigerant (106 °F), so it PULLS the pressure DOWN, air/nitrogen push it up. The maker gives no “psi per percent” figure, and a 1 °F thermometer error on R-410A is already about 3 psi, so standing pressure is only a rough check: clearly below the chart with an exact weight is a reason to recover and redo. Exact — only a lab.

Tools: Fresh vacuum pump oil, micron gauge, cap

1. Pump oil is a consumable. It absorbs water and solvent from the system; after an Rx11 flush the very first evacuation kills the oil. Cloudy, milky, smelly — the pump won't go deeper than 1000–1500 µ no matter what you do to the system.
2. Blank-off test: disconnect the pump from the system, put the micron gauge right on the pump inlet (or a short core-less hose), run it. A healthy pump with fresh oil: below 100 µ in 1–2 minutes, a good one — 20–50. Won't go below 300–500 → change the oil, repeat. Still no → vanes/seals.
3. Change oil on a hot pump: drain, fill, run a minute with the inlet open, drain, fill fresh. After a dirty system — twice. Carry a gallon of oil, not a can.
4. Open the gas ballast at the start on a wet system — water passes through the pump as vapor instead of settling in the oil; close it once the gauge reads about 1000–3000 µ (Robinair; NAVAC says 2000 µ) or you won't get depth.
5. Hoses: short, 3/8″ or 1/2″, core-less; both ports at once (liquid + suction). A 1/4″ hose with a core makes evacuation 5–10 times longer.
6. Micron gauge — only on the system, on the side away from the pump. On the pump it always looks good.

Tools: Nitrogen, micron gauge, heat gun

1. The system sat open (compressor swap, flush) — water on the walls and in the POE oil. POE absorbs moisture from air in 15 minutes and releases it under vacuum for hours.
2. Triple evacuation: pull to 1000–1500 µ → nitrogen 5–10 psi, hold 10 minutes (dry nitrogen absorbs vapor) → release to atmosphere → pull; repeat three times. Each round gets deeper.
3. Heat: compressor crankcase (a new one too — POE inside), accumulator, receiver, lower coil bends. A warm system releases moisture many times faster. Don't exceed 150 °F.
4. Cold outside (below 60 °F): under deep vacuum water freezes and stops evaporating — the microns “stick”. Nitrogen sweeps and heat are mandatory, or pull to 1500, warm, then go deeper.
5. Install the new filter drier AFTER the flush and BEFORE the final evacuation, from a sealed package, and charge within an hour of opening it — otherwise it soaks up moisture itself.
6. Decay test at the end: ≤500 µ over 10 minutes (POE), flat curve.

Tools: 1/4″ caps, micron gauge, core tool

1. Put the micron gauge on the system (the second service port or a tee at the port), not on the pump: the pump always shows 50 µ, the system shows the truth.
2. Hoses: old rubber hoses leak under vacuum by themselves; Schrader cores in the ports and in the hoses are the main source of false rise. Pull the cores with a core removal tool under vacuum or use core-less hoses.
3. Rig test: close both manifold valves, cap the hoses, evacuate the manifold with hoses and gauge to 200 µ, valve off the pump — it must hold. It rises → replace gaskets/hoses, don't chase a leak in the unit.
4. Ball-valve core removal tools beat a manifold: closed — the system is isolated from pump and hoses, the micron gauge sits on the system.
5. Only when the rig holds — draw conclusions about the system.